I just overhauled a Seth Thomas “Giant No. 1”, having an oak case 25-1/4 inches tall (job no. 4433). The movement is marked “8 1/4” but it is the same movement later called No. 89. It has between-the-plates escapement, and the plates measure 5-5/8 inches tall and 3-5/8 inches wide.
According to a repair label, it had been repaired in 1979. It had two of the overpowering USIBEL FRANCE mainsprings, 0.0180 and 0.0185 inches thick, for the time and strike, respectively. 🙁
Both mainwheels had quite noticeable tooth wear. The strike mainwheel had about twice the wear of the time mainwheel, so I turned the strike mainwheel over so the unused tooth surface could be employed. I judged that the time mainwheel would work okay as is. The time second wheel had quite a bit of wear, so I turned it over.
The previous repairer had installed 2.7 mm tall KWM bushings, which I replaced with 1.8 mm tall KWM bushings (except for the verge pivots, which get 1.4 mm high bushings). I polished the train wheel pivots before installing new bushings.
I discarded the too-strong mainsprings and used the following springs:
Time: 3/4 x 0.0155 x 96 inch Merritt’s mainspring
Strike: 3/4 x 0.0165 x 96 inch, from R & M (or Merritt’s brown box)
Even with this thin mainspring for the time side, the pendulum motion is excellent, the running arc being about 3 times the escape arc. 🙂
Note: I first tried a .0155 inch thick spring for the striking. The striking did run for at least 9 days, but the striking sounded slow, and the customer decided he wanted a faster strike. The 0.0165 inch thick spring should not cause excessive wear, but time will tell. It will certainly be better than the .0185 inch thick mainspring!
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